THE SIMPLE MUSCLE CONTRACTION 



495 



and electrodes connected as shown in the diagram, figure 351. Set the second- 

 ary coil at a position which will give a strong contraction of the muscle, and 

 record this contraction on the smoked paper of an ordinary recording cylinder. 

 Whenever the induction shock is sent through the nerve there will be a single 

 contraction of the muscle. If this contraction is recorded on the drum stand- 

 ing still, then the record will be a vertical line, the height of which can be 

 measured. From it and the arms of the lever the exact shortening of the muscle 

 can be computed. Repeat the stimulus with weaker and weaker currents, 

 until no contraction is produced. As the stimulus becomes weaker a point 



FIG. 351. Arrangement of Apparatus in the Induction Coil, as Shown for Single Inductions. 



is reached at which the contractions rapidly decrease in height and cease 

 altogether. If, on the other hand, the stimulus is stronger the contractions 

 only slightly increase. 



Arrange the apparatus so as to stimulate the muscle by an automatic key 

 attached to the recording drum. Adjust the apparatus and lever and revolve 

 the drum at a rapid rate, allowing the automatic key to be opened while the 

 drum is turning at a rapid speed. Or take a record on the pendulum myo- 

 graph, which is especially constructed for this experiment, figure 352. The 

 muscle contraction now is recorded as a wave which shows some consider- 

 able duration in t'me. Repeat the experiment, introducing a 100 double 

 vibration tuning fork to record the speed of the drum, and taking care to 

 mark the exact point on the record where the automatic key is opened. In 

 this record the muscle contraction shows three different periods or phases. 

 The first, a period of no activity, called the latent period, taking about o.oi 

 of a second; the second, the period of rapid shortening known as the con- 

 traction phase, taking about 0.04 of a second on the average; and the third, 

 a period of rapid relaxation or return to the normal, which takes about 0.05 

 of a second, see figure 353. 



The time and character of the simple muscle contraction will be influenced 

 by: i, load or tension; 2, the exact temperature; 3, by the amount of work 



